1. Field of the Invention
The present invention relates to a high-speed digital transmission method using an analog subscriber line, a subscriber accommodating system used in the high-speed digital transmission method, an accommodating device on a subscriber-terminal side and an accommodating device on an accommodating station side.
More particularly, the present invention relates to a high-speed digital transmission method using a subscriber line that allows a plurality of voice services by use of a single analog subscriber line in a call network using an xDSL technology, a subscriber accommodating system used in the high-speed digital transmission method, an accommodating device on a subscriber-terminal side and an accommodating device on an accommodating station side.
2. Description of the Related Art
Attention is being given to an xDSL (x digital subscriber line) technology in accordance with recent propagation of the Internet, wherein the XDSL is a high-speed digital transmission method using an existing telephone copper cable (subscriber line). An xDSL includes a symmetric-speed type in which an upstream speed and a downstream speed are the same, and an asymmetric-speed type in which the upstream speed and the downstream speed are different.
A symmetric-speed type xDSL is a SDSL (Single line DSL), for example. An asymmetric-speed type xDSL is an ADSL (asymmetric DSL) or a VDSL (Very high bit rate DSL), for example. In either case in which the xDSL is the symmetric-speed type or the asymmetric-speed type, simultaneous usage of a single telephone set and a single data terminal by use of a single analog subscriber line is achieved by employing a low-frequency band for a voice service and a high-frequency band for data communication.
FIG. 1 shows an example of a related art using the xDSL. This example is composed of a subscriber-terminal-side accommodating device 71, an accommodating-station-side accommodating device 72, a general data network 73, a general telephone network 74, a telephone set 75 and a data terminal 76.
The subscriber-terminal-side accommodating device 71 is an accommodating device that accommodates a plurality of subscribers, and is installed on a subscriber-terminal side (each user's house, and etc). This subscriber-terminal-side accommodating device 71 is composed of a subscriber-terminal-side splitter 54 and a subscriber-terminal-side xDSL modem 55. The subscriber-terminal-side splitter 54 separates a signal received from an analog subscriber line 53 into a low-frequency band and a high-frequency band. Additionally, the subscriber-terminal-side splitter 54 combines the low-frequency band and the high-frequency band of a signal, and transmits the signal to the analog subscriber line 53. The subscriber-terminal-side xDSL modem 55 is a modem for the data terminal 76 to carry out data communication by use of the analog subscriber line 53.
Further, the accommodating-station-side accommodating device 72 is an accommodating device that accommodates a plurality of subscribers, and is installed on an accommodating-station side (a switch station of a common carrier). This accommodating-station-side accommodating device 72 is composed of an accommodating-station-side splitter 59, an accommodating-station-side xDSL modem 60, a switch control unit 63 and a switch unit 64. The accommodating-station-side splitter 59 separates a signal received from the analog subscriber line 53 into a low-frequency band and a high-frequency band. Additionally, the accommodating-station-side splitter 59 combines the low-frequency band and the high-frequency band of a signal, and transmits the signal to the analog subscriber line 53. The accommodating-station-side xDSL modem 60 is a modem for a data terminal (not shown in the figures) connected to the general data network 73 to carry out data communication with the data terminal 76 through the analog subscriber line 53, by modulating or demodulating a signal from the data terminal connected to the general data network 73. The switch control unit 63 is a control unit that controls the switch unit 64 having a switch function.
The analog subscriber line 53 transmits voice and data. A line between the telephone set 75 and the telephone network 74 is connected by the subscriber-terminal-side splitter 54, the accommodating-station-side splitter 59 and the switch unit 64. Consequently, voice communication is carried out between the telephone set 75 and the telephone network 74.
The data terminal 76 is connected to the data network 73 by the subscriber-terminal-side xDSL modem 55, the subscriber-terminal-side splitter 54, the accommodating-station-side splitter 59 and the accommodating-station-side xDSL modem 60, and carries out data communication with the data network 73.
In a related-art telephone network, a new analog subscriber line is necessarily constructed between an accommodating station and a subscriber, every time the number of analog telephone subscribers increases. There are choices such as a BRI (Basic Rate Interface) and a PRI (Primary Rate Interface) in an ISDN (Integrated Services Digital Network). However, only two subscribers can be accommodated by use of a single analog subscriber line in the BRI. On the other hand, in the PRI, twenty-three subscribers can be accommodated by use of a single analog subscriber line, but new exclusive cables must be constructed between an accommodating station and the subscribers.
Additionally, a related-art xDSL line can accommodate a single analog telephone set and a single data terminal by use of a single analog subscriber line, but cannot accommodate more than or equal to two analog telephone sets. Accordingly, a method of accommodating a large number of analog telephone sets through a single analog subscriber line by using an existing analog subscriber line has been demanded.